Method of casting abrasive-faced articles



Jan. 10, 1933. R s EDMONDSON METHOD OF CASTI terial, which will act as aholdin same, are distributed grains of hard wear- Patented Jan. 1 0,1933 PATENT OFFICE MEIHOD OF CASTING ABRASIV E-FACED ARTICLESApplication filed March 5, 1931, Serial No. 520,465, and in GreatBritain January 26, 1931.

This invention relates to the manufacture of metal castings havingprotective or wearresistantsurfaces adapted to resist abrasion, such asstair treads, floor plates, ash chutes, paddle blades for mills, trenchor gutter covers and the like, wherein bodies or grains of hard,wear-resistant material are embedded in a metal body or casting so as tobe exposed on the surface thereof.

A well-known method of making such castings is set forth in the UnitedStates patent to Bowers No. 1,403,005; and, as there described, saidmethod includes providing a reen sand mold and coating asurface of themold, which is to give form to the protective surface of the casting,with a layer of finely divided or powdered material. On this mag bed forthe resistant material which are to form the protective orwear-resistant face of the casting. These grains may be of emery,carborunduin, alundum. or other hard mineral substance which will notfuse at the temperature of the molten metal forming the casting.

The molten metal, generally cast iron, is poured into the mold. and thegrains of wearresistant material, which are held from displacement bythe bed of finely powdered material, are surrounded by and embedded inthe metal of the casting and form thereon a wear-resistant surface.

The holding bed for the wear-resistant grains may be made of a materialwhich will fuse with themolten metal and have no influence or effectupon the surface of the casting, but preferably an infusible mineralsubstance, as fire-clay, or a material which will be consumed ordissipated by the heat of the molten metal, as rye flour, is used. Thesand of the mold is usually sprinkled with water and hence when thelayer of fire-clay powder is dusted over the wet sand, it will tend toadhere thereto, and consequently the powdered material can be readilyapplied to vertical and irregularly shaped or overhanging mold surfaces.

When fire-clay is-employed, it is preferabl sprayed with water and thusforms a so is plastic setting thruout which the wear-resistant grainsare strewn and anchored in place, the wetting of the fire-clay bed alsotending to prevent shifting of the particles thereof with reference toeach other and of the bed as a whole with relation to the mold.

This method of making metal castings having surfaces adapted to resistabrasion, while thoroughly practical, fails of perfection, however, inthat, for example, during the pouring of the molten metal into the moldsome of the grains of the Wear-resistant material will be shifted fromtheir original positions in the holding bed and bring about an unevendistribution of the grains, thus causing unnecessary crowding of thegrains in some places on the protective surface of the casting andinsuificient supply of them in other places on said surfaces. Especiallyis this true of the grains which lie on top of other grains and formsecond and third layers of the grains. Also, there sometimes happens ashifting of particles of the holding bed With reference to the mold,resulting finally in an uneven distribution of the grains of hardwear-resistant material in the finished casting. This unevendistribution of the grains produces an inefficient casting.

The object of the invention, therefore, is to provide an improved methodof making castings of the character described, in the exercise of whichmethod no shifting of the wear-resistant grains will take place andlikewise no shifting of the holding bed for the wear-resistant grainswill occur with relation to the mold surface upon which such bed rests,nor any shifting of the particles of the bed with relation to eachother.

To bring about the desired results, the holding bed and thewear-resistant grains are treated in such manner in accordance with theteachings of the invention, that the Wearresistant grains are securedfirmly to the holding bed and the individual contacting grains to eachother; and there is formed a thoroughly coherent holding bed, thepowdered particles of which are now firmly united to each other, and theunderlying particles of which are positively attached to the green sandof the mold.

In the accompanying drawing, which forms; part hereof, is illustrated amold formed according to the invention.

Of the drawing:

Fig. l is a cross-section of a mold adapted for casting an article inaccordance with the method of this invention;

Fig. 2 is a fragmentary view of the same, on an enlarged scale andshowing the application of the water glass;

Fig. 3 is a similar view after the water glass has been applied; and

Fig. l is a sectional view of a part of the finished article, castaccording to the method of the invention.

Referring to the drawing in detail, there is shown in Fig. l a mold l.comprising a drag 5 and cope 6 which. are formed to mold awear-resistant article, as a stair tread 7. On a surface 8 of the greensand of the mold i: is laid the holding bed 9, preferably formed offireclay. in which are strewn the wear-resistant grains 10.

Thefirst step in this treatment is taken preferably after the holdingbed has been sprinkled with water and the wear-res1stant grains havebeen strewn thereover, and con- Eists in spraying the wcanresistantgrains and their holding bed with a liquid 11 which has the adhesive orviscous attribute necessary to accomplish the union of the hold ng bedparticles, sand mold, and the wear-resistant grains, is-described. andwhichat the same time possesses the fluidity required to permit it to beir zled or applied efficiently to the grains and their holding bed. Theviscous liquid, like the material of the holding bed, must also be ofsuch a nature that it Wlll have no influence or effect upon the surfaceof the casting and, therefore, it may comprise infusible matter ormatter which will be fused with the molten metal poured into the moldwithout affecting the surface thereof or be consumed or dissipatedthereby. The molten metal enters the mold through the gate 12 and flowsover and about the grains 10 and thus forms the body 13 of the treadwith its resistant surface 14, as shown in Fig. 4.

It will be apparent that a liquid, possessing the viscosity oradhesiveness necessary for the purpose set forth will not possess therequired fluidity; and, therefore, the viscous liquid to be used shouldbe one that can be readily diluted with some other liquid having thenecessary fluidity; furthermore. the blended liquids shouldbe of suchnature that the diluent can be removed from the resulting compound afterthe sprinkling process therewith has been completed. It is alsoimportant that these liquids should be comparatively inexpensive so asto be commercially possible.

Specifically, according to the invention, there is employed silicate ofsoda, commonly known as water glass, and which is prepared by meltingtogether silicon dioxide and caustic soda and dissolving in water theresulting mass obtained from the fusion. The ordinary grades of waterglass contain a ratio of silica to alkali of about 3 to 1; and, whilesuch ordinary grades might be made use of, it is proposed to employ aspecial grade of water glass containing a higher ratio of silica toalkali, as will later be described. lVater glass, while itselfeconomical, has the further advantage that it is miscible with water, aquality lacking from some other substances which might otherwise beused. YVater, furthermore, is the cheapest and most common diluent.

After the wear-resistant grains have been distributed on the holdingbed, therefore, as heretofore noted, the bed and grains are sprayed withwater glass which has been di-- luted with water to the extent necessaryto permit such spraying. The diluted water glass will. penetrate betweenthe particles of the holding bed and cause them to adhere to the face ofthe mold and to each other, and, more important still, will likewisecause the wear-resistant grains to adhere firmly to the holding bed.and, when contacting, to each other.

After the application of the water glass compound to the grains andtheir holding bed, the next step in the process is to remore the diluentor water content from the compound before the molten metal comes intodirect contact therewith, as otherwise the water, under the influence ofthe heat, might cause blowing of the mold. -When ordinary grades ofwater glass are used, the water can only be removed from the compound byapplying heat thereto, as by means of a blow torch, but this is not trueof the special grade of water glass, as will presently be seen.

It may be noted at this point that when fire-clay, which is preferablyused for the holding bed in the present process, is dried or baked bythe application of heat thereto without the use in connection therewithof a suitable viscous binder, such as water glass, it will lose itsholding power and will not retain the wear-resistant grains in place. Bythe use of water glass, however, in the man ner indicated, the heat ofthe torch can be applied and not only will the water he evaporated fromthe water glass compound, but the lire-clay and water glass will bebaked or dried to form a composite mass in which the wear-resistantgrains are firmly held, and which will be firmly secured to the face ofthe mold.

Referring now to the special grade of silicate of soda to whichreference has been made and which constitutes a very important featureof the invention, it is one which contains silica to alkali in the ratioof at least 8.2 to 1 and may be produced in the ordinary way byincreasing the proportion of silica to the caustic used, when meltingthe two together. Good results have been obtained with water glasscontaining silica to alkali in a ratio as high as 4.05 to 1. A ratio of6 to 1 is even possible. In this connection, it may be stated that bysilica is meant SiO and by alkali N a O as determined by chemicalanalyses.

One important advantage of using such a special grade of water glassarises from the fact that it is capable of quick air-drying and 'doesnot require the use of the blow torch or other application of heat, andfurthermore, the viscous or adhesive nature of the cement is greaterthan in the case of water glass of the or inary grades. An even greateradvantage is that the use of this special grade of water glass does notresult in blowing of the molds when the molten metal is poured intothem, as is sometimes the case when the ordinary grades of water glassare employed. Moreover, dueto the lower percentage of alkali in thespecial grade of water glass, it has less tendency to fuse the metalwith the sand of the mold surface.

After removing the water or other diluent from the water glass compoundin the manner above described, the molten metal is poured into the moldand the casting operation completed.

It may be added that water glass, whether of ordinary grades or of thespecial grade last described, Wlll be dissipated by the heat of themolten metal when the latter is poured into the mold so as not tointerfere with the proper union of the metal with the wear-resistantgrains during the casting operation.

A brief summary of the process may be helpful. After the mold has beenprepared, the sand surface is moistened or sprinkled with water and thefire-clay in powdered form is then dusted onto the wet sand surface. Thefire-clay is next s rinkled or sprayed with water to insure the ormationof a soft plastic holding bed for the grains of wear-resistant materialwhich are then strewn upon it. the diluted water glass is now sprayedupon the holding bed and then dried to remove the water from the waterglass compound. As before noted, in the case of the special grade ofwater glass, no application of heat is necessary, since it is capable ofquick air-drying. As the final step in the rocess, molten metal ispoured into the mol to form the casting.

The invention is not limited to the precise member or sequenceof stepsor to the use of the particular materials described, as changes may bemade therein without departing from the spirit of the invention orsacrificing any of its chief advantages. For example, a variation fromthe particular method hereinbefore described consists in sprinkling alayer of coarser grains of the hard wear-resistant materials over thefirst layer of grains With the grains in place,

already secured in the holding bed and then spraying again with thewater glass after which the diluent is removed as heretofore described.These and other variations will readily suggest themselves to thoseskilled in the art now that the present process has been disclosed.

Having thus described our invention, what we claim is:

1. A method of forming a metal casting having a wear-resistant surface,which method comprises providing a mold, applying to a mold surfacethereof, which is to give form to the wear-resistant surface of thecasting, a layer composed of particles of holding material to form aholding bed for the wear-resistant material distributing grains of awearresistant material over said bed, applying to said bed and grains asolution of silicate of soda, drying said solution, and introducingmolten metal into the mold.

2. A method according to claim 1, characterized-by the fact that thesilicate of soda solution contains a ratio of silica to alkali of atleast 3.2 to 1.

3. A method according to claim 1, characterized by the fact that thesilicate of soda solution contains a ratio of silica to alkali of 4.05or above to 1.

4. A method according to claim 1, characterized by the fact that thesilicate of soda solution therein referred to contains silica andalkali, the silica content predominating and in such proportion that theblowing of the mold will be prevented when the molten metal is pouredinto the same.

5. A method according to claim 1, characterized by the fact that thesilicate of soda solution therein referred to contains silica to alkali,the silica content predpminating and in such proportion that the watermay be evaporated from the solution without the ap-

